model: Add function to expose narrow to other files.

This commit contains get_narrow() and get_narrow_length()
which are used to provide data inside narrow and length of narrow
respectively to other components of the codebase.

Author: mounilKshah

zulipterminal/model.py

@@ -341,6 +341,12 @@ def unset_search_narrow(self) -> None:
         if self.is_search_narrow():
             self.narrow = [item for item in self.narrow if item[0] != "search"]
 
+    def get_narrow(self):
+        return self.narrow
+
+    def get_narrow_length(self):
+        return len(self.narrow)
+
     def get_message_ids_in_current_narrow(self) -> Set[int]:
         narrow = self.narrow
         index = self.index